A food processor of this type is known from Patent Specification DD 217 697 A1 of the former German Democratic Republic. When cream is whipped with a food processor or mixer, there is a problem that it is hard to establish beforehand how long the cream has to be whipped to obtain a good final result. If cream whipping is stopped early, this will result in too soft whipped cream with a relatively large amount of moisture leaking out. If cream whipping is continued for too long, an irreversible process will occur in which the whipped cream rather abruptly turns into an undesired mixture of butter and skimmed milk. For a good result the whipped cream must satisfy specific quality standards. An important indicator is the volume expansion factor, that is to say, the volume expansion of the cream during whipping as a result of air inclusion. The volume expansion factor is to be about 100%. Another indicator is the moisture leakage, that is to say, the quantity of moisture leaking out of the whipped cream during a specific period of time and at a specific temperature. A high quality of whipped cream is attended by minimum moisture leakage. When the cream is being whipped it becomes ever firmer and there is a relation between the mechanical torque or the torsion necessary for cream whipping and the time elapsed. The torque time curve may coarsely be subdivided into three stages. A first stage in which the torque remains relatively low and hardly increases, a second stage in which the torque increase becomes ever steeper until a maximum torque is reached and, finally, a third stage in which the torque erratically decreases again and in which the whipped cream rather rapidly turns into butter and skimmed milk. Now it appears that if cream whipping is stopped when the maximum of the torque time curve is reached, whipped cream is obtained having minimum moisture leakage and maximum firmness. If cream whipping is stopped before the maximum is reached, a softer whipped cream is obtained which has a larger volume expansion factor and a rather large moisture leakage. The right moment to stop cream whipping depends on the user's personal preference. For soft and light cream the ideal moment lies somewhere in the steeply ascending range of the torque time curve, whereas to stop the cream whipping at the maximum of the curve will produce a firm whipped cream having little moisture leakage.
A number of methods are possible to stop cream whipping automatically at a fight moment. A first method is based on setting a fixed beating time. However, this method turns out to be insufficiently accurate for cream whipping, because the necessary period of time depends on, for example, the composition and freshness of the cream, the temperature of the cream and addition, if any, of sugar to the cream. A second method is known from the above referred to Patent Specification which discloses a food processor in which the firmness of a food mass is verified by measuring the torque necessary for driving the beater. As an indication for the torque either the motor current is measured or a torque measuring device is used in the mechanical transmission from the motor to the beater. Then a torsion signal is produced whose instantaneous value is compared at regular intervals with a Table of values stored in a non-volatile memory by a signal processing unit, which values are characteristic of the food mass. Once the torque has reached a specific value, the motor of the food processor is stopped. However, the comparison with a Table of characteristic values is not suitable as a criterion for stopping the cream whipping. As a result of the specific properties and composition of cream, such a Table can only be used if the composition, freshness, temperature and quantity of cream to be whipped correspond with the cream of the Table of characteristic values. However, in practice this is hardly ever the case.